It is desirable in various situations that means be provided for expanding a constricted vessel portion or for maintaining an open passageway through a vessel portion.
For example, these situations can be those by esophageal strictures that are caused by esophageal carcinoma or esphageal metastasis, or those by strictures that resulted from the cancer of biliary system, urinary duct system and bronchial system.
The balloon expansion has been well known method of enlarging and maintaining the passageway of esophagus in these cases; but this method should be operated repeatedly for its temporary effects, and also it has no effects on the patients of serious strictures.
As alternatives, various artificial-esophagi have been used in the cases of esophageal strictures, but since they have no constriction and relaxation, the rate of esophageal rupture is high (30-40%) in the process of inserting them into the strictural area that has been caused by the cancer, and the high mortality rate due to mediastinitis results from rupture of esophagus. In addition, the patient has a great difficulty in swallowing due to narrow inner diameter (10-12 mm) of artificial esophagus, and obstruction of artificial-esophagus occurred frequently due to food intake.
As the means of overcoming the difficulty, a device to hold the passageway enlarged using a stent was presented by U.S. Pat. No. 4,214,587. However, the device of the invention has the temporary effect in enlarging the passageway, there is still the problem that the endovascular lumen gets narrows after a long time.
To improve this disadvantages, U.S. Pat. No. 4,580,568 was offered. The stent of said invention includes a wire formed into a closed zig-zag configuration including an endless series of straight sections joined by bends. The stent is resiliently compressible into a smaller first shape wherein the straight sections are arranged side-by-side and closely adjacent one another for insertion into a larger second shape wherein said straight sections press against the walls of the passageway to maintain it open.
However, in a case that the stent of the U.S. Pat. No. 4,580,568 invention is put into use for a long time, it still has the problem that the lumen is narrowed, because the proliferated cells cover the stent thickly. There is no effect in the case of the stricture by cancer, because the cancer cells can pass through the straight sections.